If 40.0 g of hcl react with an excess of magnesium metal, what is the theoretical yield of hydrogen?

The balanced reaction is:

Mg (s) + 2HCl (aq) --> MgCl 2 (aq) + H 2 (g) 

We are given the amount hydrochloric acid to be used for the reaction. This will be the starting point of the calculation.

40.0 g HCl ( 1 mol HCl / 36.46 g HCl) (1 mol H2 / 2 mol HCl) (2.02 g H2 / 1 mol H2) = 1.11 g H2

i do not get it   at all